Personal watercraft are typically constructed by attaching a deck to a hull to form an engine compartment therebetween. The propulsion systems for these personal watercraft normally include an inboard-mounted, internal combustion engine and a jet propulsion unit in the form of an impeller assembly positioned in a tunnel open to the underside and the stern of the hull. Due to the compact size of personal watercraft, limited space is available within the hull.
The compactness of personal watercraft presents a number of unique design problems. One such design problem is the layout of the exhaust system for discharging exhaust gases generated by the engine. This problem is rendered particularly acute because, as is typical with marine propulsion systems, the engine exhaust gases are typically discharged to the atmosphere either at, below or close to the water level depending on the speed of the watercraft. For example, at slow speeds the exhaust outlet may be below the waterline. At high speeds, the exhaust outlet is located at a higher position and may be above the waterline. Due to this location of the exhaust outlet, care must be taken to ensure that water cannot enter the engine through the exhaust system. This problem is compounded because there is a possibility that the watercraft could capsize. Therefore, when capsized and subsequently righted, an adequate exhaust system design ensures that any water that has entered the exhaust system is prevented from finding its way into the engine. Additionally, under normal operating conditions, the exhaust system must be designed to inhibit coolant water that is directed into the muffler via a water jacket or water injection from entering the engine.
Therefore, there is a need for a relatively compact exhaust system for a personal watercraft that helps prevent the entry of water into the engine. There is also a need for a personal watercraft having such an exhaust system.